DE102020212402A1 - Device and method for cooling a heat exchanger - Google Patents

Abstract

The invention relates to a device (10) and a method for cooling a heat exchanger (12) of a fuel cell (16) of an aircraft engine outside of a flight phase of an aircraft. The flight engine has an air line (20) with at least one compressor (21, 22, 23) for supplying compressed air for operating the fuel cell (16). A flow amplifier (40) is arranged in a region of the heat exchanger (12) which is adapted to direct air onto a cooling surface (13) of the heat exchanger (12), thereby dissipating heat energy from the cooling surface (13) of the heat exchanger (12). will.

Description

The invention relates to a device and a method for cooling a heat exchanger of a fuel cell of an aircraft engine outside of a flight phase of an aircraft, the aircraft engine having an air line with at least one compressor for supplying compressed air to operate the fuel cell.

In flight engines with fuel cells, large amounts of heat are generated which have to be dissipated via heat exchangers in order to prevent the fuel cells from overheating. Correspondingly, heat exchangers of such aircraft drives are usually arranged in such a way that propeller downwash (downwash air) and/or ram air can be used to cool the at least one heat exchanger. On the ground, outside of a flight phase of an aircraft, no cooling air or an insufficient amount of cooling air is available from this. During operation of the fuel cells outside of a flight phase of the aircraft, alternative cooling of the heat exchangers is therefore necessary in order to dissipate sufficient heat from the fuel cells. Additional fans (fans) arranged on the aircraft to generate a flow of cooling air on the ground are superfluous during the flight phase and have an aerodynamically disadvantageous effect.

Proceeding from this, it is an object of the present invention to propose an improved device and a method for cooling a heat exchanger of a fuel cell of an aircraft engine outside of a flight phase of an aircraft. According to the invention, this is achieved by the teaching of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

To solve the problem, a device for cooling a heat exchanger of a fuel cell of an aircraft engine is proposed in a first aspect when an aircraft is not in flight, the aircraft engine having an air line with at least one compressor for supplying compressed air for operating the fuel cell. The device has a flow amplifier arranged in the area of the heat exchanger, which is designed to direct air onto a cooling surface of the heat exchanger, and a branch in the air line arranged after the at least one compressor, via which compressed air can be routed to the flow amplifier.

Similar to conventional turbomachines powered by kerosene, a fuel cell in an aircraft engine also requires compressed air in order to achieve high power density. Electrochemical fuel cells convert fuel and oxidant into electrical energy and a reaction product. Ambient air, which is usually used as an oxidizing agent in aircraft propulsion, is supplied to the fuel cell via an air line which, in addition to the necessary lines, connections and valves, also has at least one compressor for compressing air sucked in from the environment. One or more compressors or compressor stages arranged in series and/or in parallel can be provided for compressing the air. Because the reaction of fuel and oxidant produces both heat and electricity, even after a fuel cell stack has reached an operating temperature, it must be cooled to avoid damaging the fuel cells.

Such cooling usually takes place with the aid of at least one heat exchanger connected to a coolant circuit of the fuel cells, over which a fan and/or ram-air flow flows during the flight phases. In this case, an air flow flowing over a cooling surface of the heat exchanger, in particular, absorbs heat and dissipates it, in particular convectively, from the heat exchanger. Although “the heat exchanger” is specified in the claims and the description, within the scope of the invention the heat exchanger can of course also have several heat exchanger devices arranged spatially next to one another and/or distributed, which in particular can also (each) have several cooling surfaces. In this context, a cooling surface is any (surface) surface arranged on the heat exchanger which is heated by the thermal energy to be dissipated and from which heat can be dissipated with an air flow sweeping over it. Since the fuel cells of the flight propulsion system are at least partly operated outside of the flight phase, for example to provide propulsion energy for taxiing on the runway or to supply power to the aircraft on the ground, there is insufficient fan or ram pressure air flow to dissipate heat energy from the aircraft during these phases Heat exchangers of the fuel cells available.

In order to direct the air to a cooling surface of the heat exchanger, the proposed device has a flow amplifier arranged in the area of the heat exchanger. Outside of the flight phases, the fuel cells are usually only operated at reduced power, which is why only a reduced air supply to the fuel cells is required. Accordingly, there is then free compressor power available, which is used to cool the heat exchanger of the burner fabric cells can be used. For this purpose, the proposed device in the air line of the fuel cell has a branching arranged after the at least one compressor, via which compressed air can be branched off from the air line and routed to the flow booster. Depending on the structure and the performance of the compressor, the branching can be arranged after a first or further compressor, in particular also depending on the control-technical integration of the branching circuit during the transition into or out of a flight phase. For example, only part of the compressed air available at the branch can be removed via the branch, or the air available in a partial branch of the compressor can be routed to the flow amplifier.

The compressed air discharged via the branch is guided from there to a flow amplifier which is arranged in the area of the heat exchanger and is designed to guide the air onto a cooling surface of the heat exchanger. The flow amplifier is arranged in the area of the heat exchanger and is therefore in a suitable position for directing the increased air flow onto at least one cooling surface of the heat exchanger. In particular, the flow intensifier has an air outlet opening with suitable outlet geometries and/or air guiding devices in order to form an air flow that is advantageous in particular with regard to the flow speed and direction for efficient removal of thermal energy from the heat exchanger. In particular, the compressed air guided through the flow booster has a higher flow speed after exiting the flow booster than before the flow booster. Such a flow intensifier can have different geometries and flow cross-sections adapted to the specific place of use. Accordingly, the flow amplifier can be adapted to the space available, which is why such flow amplifiers can also be arranged in narrow spaces and still achieve good air flow guidance. In particular, a flow amplifier is designed and arranged in such a way that it does not have an aerodynamically disadvantageous effect during the flight phase.

As a result, the proposed device enables heat energy to be removed from a heat exchanger of a fuel cell of an aircraft engine outside of an aircraft flight phase without additional complex devices for generating an air flow, which are superfluous during the flight phase or have an aerodynamically disadvantageous effect. To remove the heat energy from the heat exchanger outside the flight phase, an existing compressor capacity that is not required on the ground is used to compress the air, which can be used to remove the excess heat energy. In this way, only a few additional devices are required for cooling the heat exchanger of the fuel cells outside of the flight phases.

In one embodiment of the device, the flow amplifier works according to the Venturi and/or the Coanda principle in order to direct the air onto the cooling surface of the heat exchanger. In addition, in addition to the compressed air, the device can also direct ambient air onto the cooling surface of the heat exchanger. For example, the flow amplifier can be designed in such a way that it uses the effect of a (Venturi) jet pump. The air flow supplied by the compressor forms the driving medium, so that additional ambient air can be sucked in and accelerated in the area of the flow booster before the increased air flow formed flows to the cooling surface of the heat exchanger. Alternatively or in combination with this structure, the flow amplifier can have, for example, an outlet opening using the Coanda principle, in which the air flow is guided over the surface of a suitably widening wall, against which the air flow nestles. This results in a pressure drop in the center of the outlet opening, through which additional ambient air can be sucked in and accelerated before the increased air flow formed flows to the cooling surface of the heat exchanger. The amount of heat that can be removed by the heat exchanger can be increased by using the Venturi and/or the Coanda principle.

In one embodiment of the device, a flow control valve is arranged in front of the flow booster, with which the air flow supplied to the flow booster can be regulated. With the help of a flow control valve, the flow rate of a flow booster can be regulated in a simple manner in order to adapt it to the cooling air requirement of the heat exchanger in particular. For example, a flow control valve can be arranged in the branching of the air line.

In one embodiment of the device, the flow intensifier is at least partially ring-shaped. In such an embodiment, the air flow can be guided, for example, through an annular duct, which has an outlet opening on its radial inner side that is oriented essentially parallel to the direction of the axis of rotation. In this embodiment, in the center of the axial air flow formed as a result, a negative pressure is created, through which ambient air is sucked in, which intensifies the air flow formed in the direction of the heat exchanger. A directed air flow with an at least partially circular cross section can be formed with such an embodiment.

In one embodiment of the device, the heat exchanger is arranged in the drive nacelle. This means that it is positioned in close proximity to the fuel cells in the drive pod (nacelle) and their coolant supply. In this embodiment of the device, the flow booster can be arranged, for example, in the inlet of the drive nacelle, so that an air stream flowing out of the flow booster flows through the drive pod axially. When flowing through the propulsion nacelle, the air flow can use the flow paths provided for the cooling air flow during the flight phase in order to reach the at least one cooling surface of the heat exchanger and to transport the heat absorbed there out of the propulsion nacelle.

In one embodiment of the device, the compressor has a multi-stage design and the branching is arranged after at least a first stage. The multi-stage compressor for supplying air to the fuel cells can have a number of compressor stages arranged in series and/or in parallel, which are used outside of the flight phases, for example only partially to supply other devices of the aircraft with cooling air. For example, individual compressor stages can be switched off outside of the flight phase, since they are not required to compress the lower air volume required. Correspondingly, the branch for branching off compressed air for the flow booster is arranged in such a way that the supply of the flow booster is ensured and can be integrated in a suitable manner into the control of the compressor.

• - Komprimieren von Luft mit wenigstens einem Kompressor des Flugantriebs;
• - Leiten der komprimierten Luft durch einen Strömungsverstärker auf eine Kühlfläche des Wärmetauschers;
• - Aufnehmen der Wärmeenergie von der Kühlfläche durch den Luftstrom; und
• - Abführen der Wärmeenergie mit den Luftstrom.

To achieve the object, a second aspect proposes a method for cooling a heat exchanger of a fuel cell of an aircraft engine outside of a flight phase of an aircraft, the aircraft engine having an air line with at least one compressor for supplying compressed air for operating the fuel cell. The procedure has the following steps:

• - Compressing air with at least one compressor of the flight engine;
• - directing the compressed air through a flow amplifier onto a cooling surface of the heat exchanger;
• - absorption of thermal energy from the cooling surface by the air flow; and
• - Dissipation of the thermal energy with the air flow.

In the proposed method, air is first compressed with a compressor of the flight engine. This can be a compressor, for example, which is used to compress the air required for the operation of the fuel cell, which air is supplied to the fuel cell via an air line. Since the fuel cells are usually only operated with reduced power outside of the flight phases, only a reduced air supply to the fuel cells is required. Free compressor power is thus available, which can be used to compress air for cooling the heat exchanger of the fuel cells. In the proposed method, the compressed air is guided to a flow amplifier which is arranged in particular in the area of the heat exchanger and which directs the air onto at least one cooling surface of the heat exchanger.

The flow amplifier models the flow profile of the air flow, in particular with regard to the flow speed and direction, in such a way that as much thermal energy as possible can be absorbed and dissipated by the cooling surface of the heat exchanger. In this way, thermal energy can be removed efficiently from the heat exchanger. In particular, the compressed air guided through the flow booster has a higher flow speed after exiting the flow booster than before the flow booster.

The proposed method thus enables thermal energy to be removed with little effort from a heat exchanger of a fuel cell of an aircraft engine outside of a flight phase of an aircraft, using at least some of the already existing aircraft engine devices. The method can be carried out in particular with the device described above, which can have the features of one or more of the embodiments described for this purpose. The method can accordingly also have the features and advantages described for this purpose.

In one embodiment of the method for cooling a heat exchanger, the flow amplifier also directs ambient air onto a cooling surface of the heat exchanger in addition to the compressed air. The flow amplifier sucks in ambient air, which is accelerated by the air flow fed to it. The air flow, which is additionally strengthened in this way, then flows to the cooling surface of the heat exchanger in order to absorb and dissipate thermal energy from its cooling surface(s). on in this way, the amount of heat that can be removed by the heat exchanger can be increased.

• 1 eine schematische Darstellung einer beispielhaften erfindungsgemäßen Vorrichtung zum Kühlen eines Wärmetauschers einer Brennstoffzelle eines Flugantriebs außerhalb einer Flugphase eines Flugzeugs;
• 2 eine schematische Schnittdarstellung eines beispielhaften Strömungsverstärkers; und
• 3 eine schematische Darstellung eines Ablaufdiagramms des erfindungsgemäßen Verfahrens.

Further features, advantages and possible applications of the invention result from the following description in connection with the figures. It shows

• 1 a schematic representation of an exemplary device according to the invention for cooling a heat exchanger of a fuel cell of an aircraft engine outside of a flight phase of an aircraft;
• 2 a schematic sectional view of an exemplary flow amplifier; and
• 3 a schematic representation of a flowchart of the method according to the invention.

1 shows a schematic representation of an exemplary device 10 according to the invention for cooling a heat exchanger 12 of a fuel cell 16 of an aircraft engine outside of a flight phase of an aircraft. The flight engine has an air line 20 for supplying the fuel cell 16 with air. In the exemplary embodiment shown, the air line 20 has three compressors 21, 22, 23 or compressor stages 21, 22, 23 for supplying compressed air for operating the fuel cell 16. Two of the compressors 21, 22 or compressor stages 21, 22 are connected in parallel in the exemplary embodiment, and another compressor 23 or compressor stage 23 is connected in series with them. This compressor 23 or compressor stage 23 is additionally driven by a turbine 24, which is subjected to rotary energy by the air flow conducted through the cathode(s) 17 of the fuel cell(s) 16 before the air escapes from the air line 20 via an air outlet 25 . The ambient air is fed to the air line 20 via an air filter 26 .

The fuel cell 16 is cooled via a cooling circuit 30 which has a coolant reservoir 31 , a filter 32 , a coolant pump 33 and an air-cooled heat exchanger 12 for cooling the fuel cell 16 . The coolant is pumped by the coolant pump 33 through the fuel cell 16, where it absorbs thermal energy. The cooling surfaces 36 of the heat exchanger are flown over by a flight air flow during a flight phase of the aircraft, which flow energy generated in the fuel cell 16 dissipates.

In order to dissipate excess heat energy from the fuel cell 16 outside of the flight phases, the device 10 for cooling the heat exchanger 12 has a flow amplifier 40 which is arranged in the area of the heat exchanger 12 and is designed to direct air onto a cooling surface 13 of the heat exchanger 12. The flow amplifier 40 is supplied with compressed air from the air line 20, which primarily serves to supply the fuel cell 16 during the flight phase and is usually not fully utilized outside of the flight phase. For this purpose, after at least one compressor 21, 22, a branch 28 is arranged in the air line 20, via which, in the exemplary embodiment, air compressed by the compressors 21 and 22 can be routed to the flow amplifier 40. In the exemplary embodiment, a flow control valve 29 is arranged upstream of the flow booster 40, with which the air flow fed to the flow booster 40 can be regulated.

2 shows a schematic sectional view of an exemplary flow amplifier 40, which is ring-shaped. The air flow branched off from the air line 20 is guided through an annular air duct 41 which has an outlet opening 42 on its radial inner side which is directed essentially parallel to the direction of the axis of rotation. The air flow is guided over the surface of the widening wall, against which the flow 44 nestles according to the Coanda principle. In the process, a negative pressure forms in the center of the flow intensifier 40, as a result of which ambient air 45 is additionally sucked in and accelerated axially. The intensified air flow formed in this way then flows to the cooling surface 13 of the heat exchanger 12 in order to absorb thermal energy and thus dissipate it from the heat exchanger 12 .

3 FIG having.

The method according to the invention has the following steps: In a first step a), air is compressed with at least one compressor 21, 22, 23 of the flight engine and in a second step b) is conducted through a flow amplifier 40 onto a cooling surface 13 of the heat exchanger 12. In one embodiment of the method, the flow amplifier 40 can also direct ambient air onto a cooling surface 13 of the heat exchanger 40 in addition to the compressed air in a step b1). In a step c), the air flow absorbs the thermal energy from the cooling surface 13 of the heat exchanger 12 and, in a further step d), dissipates it from the cooling surface of the heat exchanger.

reference list

10

contraption

12

heat exchanger

13

cooling surface

16

fuel cell

17

cathode

20

as the crow flies

21

Compressor (stage)

22

Compressor (stage)

23

Compressor (stage)

24

turbine (stage)

25

air outlet

26

air filter

28

branch

29

flow control valve

30

cooling circuit

31

coolant storage

32

filter

33

coolant pump

40

flow booster

41

air duct

42

exhaust port

44

flow

45

ambient air

Claims (10)

Device (10) for cooling a heat exchanger (12) of a fuel cell (16) of an aircraft engine outside of a flight phase of an aircraft, the aircraft engine having an air line (20) with at least one compressor (21, 22, 23) for supplying compressed air for operation of the fuel cell (16), characterized by a flow amplifier (40) arranged in the region of the heat exchanger (12), which is designed to direct air onto a cooling surface (13) of the heat exchanger (12) and by a compressor ( 21, 22, 23) arranged branch (28) in the air line (20), via which compressed air to the flow amplifier (40) can be routed. device after claim 1 , characterized in that the flow amplifier (40) works according to the Venturi and/or the Coanda principle in order to direct the air onto the cooling surface (13) of the heat exchanger (40). device after claim 2 , characterized in that the flow amplifier (40) is set up to conduct not only the compressed air but also ambient air (45) onto the cooling surface (13) of the heat exchanger (12). Device according to one of the preceding claims, characterized in that a flow control valve (29) is arranged upstream of the flow booster (40), with which the air flow supplied to the flow booster (40) can be regulated. Device according to one of the preceding claims, characterized in that the flow intensifier (40) is at least partially ring-shaped. Device according to one of the preceding claims, characterized in that the heat exchanger (12) is arranged in the drive gondola. device after claim 6 , characterized in that the flow amplifier (40) is arranged in the inlet of the drive nacelle. Device according to one of the preceding claims, characterized in that the compressor (21, 22, 23) is constructed in several stages and the branch (28) is arranged after at least a first stage (21, 22, 23). Method for cooling a heat exchanger (12) of a fuel cell (16) of an aircraft engine outside of a flight phase of an aircraft, the aircraft engine having an air line (20) with at least one compressor (21, 22, 23) for supplying compressed air for operating the fuel cell ( 16), characterized by the steps: - Compressing air with at least one compressor (21, 22, 23) of the flight engine; - Passing the compressed air through a flow amplifier (40) onto a cooling surface (13) of the heat exchanger (12); - absorbing the thermal energy from the cooling surface (13) by the air flow; and - removing the thermal energy with the air flow. Method for cooling a heat exchanger according to claim 9 , characterized in that the flow amplifier (40) directs not only the compressed air but also ambient air (45) onto a cooling surface (13) of the heat exchanger (12).

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